In recent years, a capsule endoscope having an imaging function and a radio communication function has appeared in the field of endoscope. The capsule endoscope is swallowed by a subject from the mouth for an observation (examination), moves within internal organs (within body cavities) such as a stomach and a small intestine, along peristaltic motions thereof, and sequentially images using the imaging function, until naturally discharged from the body (human body).
During the observation period while the capsule endoscope is moving within the internal organs, image data acquired within the body cavity by the capsule endoscope is sequentially transmitted to the outside of the subject by the radio communication function such as radio communication, and is stored in a memory provided within a receiving apparatus outside. When the subject carries the receiving apparatus having the radio communication function and the memory function, the subject can move freely even during the observation period after swallowing the capsule endoscope until the capsule endoscope is discharged. After the observation, a doctor or a nurse can perform diagnosis by displaying the images of the body cavity onto a display unit such as a display, based on the image data stored in the memory of the receiving apparatus.
In general, a receiving apparatus has plural antennas disposed dispersedly at the outside of the subject to receive image signals transmitted from the capsule endoscope, and selectively switches one antenna having a small error in the reception of the image signal to receive the image signal. Patent Document 1 describes a receiver that switches between plural antennas disposed at the outside of a subject for reception, and locates a position of a capsule endoscope within the subject as a transmission source of the image signal, based on electric-field strength that each antenna receives.
Patent Document 1: Japanese Patent Application Laid-open No. 2003-19111